A government shutdown will have far-reaching consequences for some, but minimal impact on others.
Mail will still be delivered. Social Security and Medicare benefits will continue to flow.
But vacationers will be turned away from national parks and Smithsonian museums. Low-to-moderate income borrowers and first-time homebuyers seeking government-backed mortgages could face delays.
Here is a look at how services are and are not being affected since Congress failed to reach an agreement averting a government shutdown.
Federal air traffic controllers remain on the job and airport screeners will keep funneling passengers through security checkpoints. Federal inspectors will continue enforcing safety rules.
The State Department will continue processing foreign applications for visas and U.S. applications for passports, since fees are collected to finance those services. Embassies and consulates overseas will continue to provide services to American citizens.
Social Security and Medicare benefits will keep coming, but there could be delays in processing new disability applications. Unemployment benefits will still go out.
Federal courts will continue operating normally for about 10 business days after the start of a shutdown, roughly until the middle of October. If the shutdown continues, the judiciary will have to begin furloughs of employees whose work is not considered essential. But cases will continue to be heard.
Deliveries will continue as usual because the U.S. Postal Service receives no tax dollars for day-to-day operations. It relies on income from stamps and other postal fees to keep running.
All national parks will be closed, as will the Smithsonian museums, including the National Zoo in Washington. Visitors using overnight campgrounds or other park facilities will be given 48 hours to make alternate arrangements and leave the park. Among the visitor centers that will be closed: the Statue of Liberty and Ellis Island in New York, Independence Hall in Philadelphia, Alcatraz Island near San Francisco and the Washington Monument.
New patients will not be accepted into clinical research at the National Institutes of Health, but current patients will continue to receive care. Medical research at the NIH will be disrupted and some studies will be delayed. The Centers for Disease Control and Prevention will be severely limited in spotting or investigating disease outbreaks, from flu to that mysterious MERS virus from the Middle East.
The Food and Drug Administration will handle high-risk recalls suspend most routine safety inspections. Federal meat inspections are expected to proceed as usual.
A small number of Head Start programs, about 20 out of 1,600 nationally, will feel the impact right away. The federal Administration for Children and Families said grants expiring about Oct. 1 would not be renewed. Over time more programs will be affected. Several of the Head Start programs that will immediately feel the pinch are in Florida. It's unclear if they will continue serving children.
The Special Supplemental Nutrition Program for Women, Infants and Children, known as WIC, could shut down. The program provides supplemental food, health care referrals and nutrition education for pregnant women, mothers and their children.
School lunches and breakfasts will continue to be served, and food stamps, known as the Supplemental Nutrition Assistance Program, or SNAP, will continue to be distributed. But several smaller feeding programs will not have the money to operate.
Americans would still have to pay their taxes and file federal tax returns, but the Internal Revenue Service says it will suspend all audits. Got questions? Sorry, the IRS says taxpayer services, including toll-free help lines, will be shut as well.
Many low-to-moderate incomes borrowers and first-time homebuyers seeking government-backed mortgages could face delays during the shutdown. The Federal Housing Administration, which guarantees about 30 percent of home mortgages, won't underwrite or approve any new loans during the shutdown. Action on government-backed loans to small businesses will be suspended.
NASA will continue to keep workers at Mission Control in Houston and elsewhere to support the International Space station, where two Americans and four others are deployed. The National Weather Service will keep forecasting weather and issuing warnings and the National Hurricane Center will continue to track storms. The scientific work of the U.S. Geological Survey will be halted.
The majority of the Department of Homeland Security's employees are expected to stay on the job, including uniformed agents and officers at the country's borders and ports of entry, members of the Coast Guard, Transportation Security Administration officers, Secret Service personnel and other law enforcement agents and officers. U.S. Citizenship and Immigration Services employees will continue to process green card applications.
The military's 1.4 million active duty personnel will stay on duty and still be paid on time as a result of legislation passed by Congress and signed by President Obama. About half of the Defense Department's 800,000 civilian employees will be furloughed.
All 116 federal prisons will remain open, and criminal litigation will proceed.
Most services offered through the Department of Veterans Affairs will continue because lawmakers approve money one year in advance for the VA's health programs. Veterans will still be able to visit hospitals for inpatient care, get mental health counseling at vet centers or get prescriptions filled at VA health clinics. Operators will still staff the crisis hotline and claims workers will still process payments to cover disability and pension benefits. But those veterans appealing the denial of disability benefits to the Board of Veterans Appeals will have to wait longer for a decision because the board will not issue any decisions during a shutdown.
Federal occupational safety and health inspectors will stop workplace inspections except in cases of imminent danger.